1. Field of the Invention
The present invention relate to a liquid crystal display and a method of driving the same.
2. Discussion of the Related Art
Active matrix type liquid crystal displays display a moving picture using a thin film transistor (TFT) as a switching element. The active matrix type liquid crystal displays have been implemented in televisions as well as display devices in portable devices, such as office equipment and computers, because of the thin profile of the active matrix type liquid crystal displays. Accordingly, cathode ray tubes (CRT) are being rapidly replaced by the active matrix type liquid crystal displays.
The active matrix type liquid crystal display includes data lines and gate lines crossing each other, and liquid crystal cells arranged at each crossing of the data lines and the gate lines in a matrix format. A thin film transistor (TFT) is formed at each crossing of the data lines and the gate lines. As shown in FIG. 1, data driver integrated circuits (ICs) of a liquid crystal display supply a positive or negative data voltage to data lines during low logic periods of a source output enable signal (SOE). Gate driver ICs of the liquid crystal display sequentially supply gate pulses that are synchronized with the positive/negative data voltage to gate lines G1 to G3 during low logic periods of a gate output enable signal (GOE). Hence, a liquid crystal cell of 1 line charged to the data voltage is selected.
If a DC voltage is applied to a liquid crystal layer of the liquid crystal display for a long time, negative ions move in the same vector direction and positive ions move in a vector direction opposite the vector direction of the negative ions based upon a polarity of an electric field applied to liquid crystals. Hence, the ions in the liquid crystal layer are polarized. As time elapses, the accumulation amount of negative ions and the accumulation amount of positive ions increase. As a result, an alignment layer is degraded and alignment characteristics of the liquid crystal are also degraded. In other words, the application of the DC voltage to the liquid crystal layer for a long time causes stains on the display screen, and the size of the stains increases as time elapsed. To solve the stain problem, a liquid crystal material with a low dielectric constant has been developed, or a method for improving an alignment material or an alignment method has been attempted. However, it takes a long time and great expense to develop a material used in the method. Further, the use of the liquid crystal material with the low dielectric constant may reduce drive characteristics of the liquid crystal. According to the experimental findings, as the amount of impurities ionized inside the liquid crystal layer increases and an acceleration factor becomes large, an appearance time of the stains becomes more rapid. The acceleration factor may include a temperature, time, a DC drive of the liquid crystal, and the like. For example, when a period during which a DC voltage of the same polarity is applied to the liquid crystal layer becomes longer at a high temperature, the stains worsen and the appearance time of the stains becomes more rapid. Because the stains non-uniformly appear between display panels manufactured through the same manufacture line, the stain problem cannot be solved only by development of new material or an improvement of process.